Interpretive Summary: Many important fungal pathogens reside in the soil and infect roots of crops often causing significant yield losses. Sudden death syndrome (SDS) is an economically important soybean disease caused by the soilborne pathogen Fusarium solani f. sp. Glycines that occurs in most soybean producing states in the U.S. A molecular technique, called the polymerase chain reaction (PCR) method was used to detect nucleic acid, known as DNA from F. solani f. sp. glycines. Specificity of the technique to detect F. solani f. sp.glycines was successful and did not falsely detect DNA from other soybean fungal pathogens and soybean. F. solani f. sp. glycines DNA was detected in field-grown soybean roots and soil by PCR. F. solani f. sp. glycines was detected in all soil samples from five Illinois Agricultural Statistic Districts including 100, 89, 50, 92 and 50% of the samples from East, Central, Northeast and West Districts, respectively. The molecular method developed for the specific detection of F. solani f. sp. glycines DNA produced data on its occurrence either from symptomatic or asymptomatic plants and soil. This information is useful to scientist developing techniques to detect pathogens from different ecosystems and to epidemiologist that would be interested in monitoring the spread of pathogens by this type of detection system.

Technical Abstract:
A polymerase chain reaction (PCR)-based method was developed to detect DNA of Fusarium solani f. sp. glycines, the cause of soybean sudden death syndrome. Two pairs of primers, Fsg1/Fsg2 designed from the mitochondrial small subunit ribosomal RNA gene, and sgEF1/FsgEF2 designed from the translation elongation factor 1-a ene, produced PCR products of 438 and 237 bp, respectively. Primer specificity was tested with DNA from 82 F. solani f. sp. glycines, 55 F. solani non-SDS isolates, 43 other soybean fungal pathogens, and soybean. sensitivity of primer Fsg1/Fsg2 was 10 pg while sensitivity of FsgEF1/FsgEF2 was 1 ng when using F. solani f. sp. glycines total genomic DNA or down to 103 macroconidia per g of soil. Nested-PCR increased the sensitivity of primers 1,000 fold to 10 fg for primers Fsg1/Fsg2 and 1 pg for primers FsgEF1/FsgEF2. F. solani f. sp. glycines DNA was detected in field-grown soybean roots and soil by PCR using either single pairs of primers or the combination of two pairs of primers. The occurrence of F. solani f. sp. glycines was determined using nested-PCR for 47 soil samples collected from soybean fields in 20 counties of Illinois in 1999. F. solani f. sp. glycines was detected in all soil samples from five Illinois Agricultural Statistic Districts including 100, 89, 50, 92 and 50% of the samples from East, Central, Northeast and West Districts, respectively. The molecular method developed for the specific detection of F. solani f. sp. glycines DNA produced data on its occurrence either from symptomatic or asymptomatic plants and soil.